Wx 301 final exam || 100% Correct Solutions.
Identify the favored regions around a winter mid-latitude cyclone for the formation of snow and
other types of frozen precipitation correct answers North west of the low/ ahead of the warm
front
Describe how the temperature must change with height to produce rain, snow, sleet, or freezing.
correct answers Depends on the thickness of the layer near the surface.
Define critical thickness correct answers Thickness you need for snow/540 decameters/5,400
meters
Analyze a 1000-500mb thickness chart to determine the likelihood of rain versus snow. correct
answers The lower the thickness, the colder the better the chances of having snow Think 540 as
32 degrees mark bare minimum.
Define what is meant by ground icing "hold-over" times. correct answers • Hold-over time:
length of time deicing fluid will prevent ice build-up on an aircraft
• Time ranges from 45 minutes for frost to less than a couple minutes for freezing rain
Explain why equivalent liquid water precipitation rate is important in aviation winter weather
decision-making and how it affects hold-over times. correct answers • Basing precipitation
intensity on visibility alone does not adequately measure true rate of liquid water equivalent
accumulation
• Accurate, real-time measurements of liquid-equivalent snowfall rates need to be made and
reported to pilots and ground operations personnel, not just visibility measurements.
• Accurately predicting deicing hold-over times remains a significant aviation safety factor
Identify the fundamental cause of icing correct answers • Liquid water droplets +5 to -40c
Rime ice correct answers small droplets, freeze rapidly cause trapped air, opaque appearance,
forms at temps below -15C
clear ice correct answers larger droplets with little trapped air, forms at 0 to -5 C, equivalent to
freezing rain
mixed Ice correct answers Mixed: drop size varies, forms at intermediate temps -5 to -15C
Describe the impacts of icing on aircraft performance (stall speed, fuel consumption, service
ceiling, stall angle, etc) correct answers • Stall speed increases
• Fuel rate consumption increases
• Service ceiling decreases
• Stall at lower angle of attack than normal
• Friction increases
, Describe the effects exposure time on ice buildup. correct answers • Longer exposure time =
more icing
Describe the relationship between wing size and performance degradation due to icing correct
answers Thin wings collect more ice than large wings
• A large transport aircraft will build proportionally less ice than a small aircraft going through
the same icing region
Describe super-cooled large droplets (SLDs) and runback icing as well the hazards they pose
correct answers Small ice crystals form within droplet which may cause the entire drop to freeze
Causes a large freezing cluster of ice to form on a surface
Identify the favored areas for icing near mountains correct answers • Worst icing near the peaks
and windward side
Describe the range of temperatures and relative humidities where icing is most commonly
observed. correct answers • Most common between 0C and -40C; in-cloud humidity 70-100%
• Mountains (orographic lift), cumulus clouds and thunderstroms (strong updrafts), areas of sleet
• NW of the low, ahead of the warm front, and near the cold front
Identify the icing severity/intensity level where deicing/anti-icing equipment become ineffective.
correct answers Severe: found in stratus clouds / downwind of large bodies of water, and when
the clouds are lifted by convection over water or mountains, they become stratocumulous. That
can mean thick layer of mixed, clear, and rime icing
Identify the requirements for sustaining icing in a mixed cloud environment. correct answers
Updrafts, super-cooled liquid droplets, low temperature
Describe the safest courses of action for avoiding icing in stratiform vs. cumuliform cloud
environments correct answers Highest liquid water content at cloud top
Decode basic icing symbols. correct answers Slight - 1 bar
Moderate - 2 bars
Severe - 3 bars
Describe the CIP correct answers • Current Icing Conditions, uses PIREPs, forecasts, and
observations
• Current icing potential; FAA supplementary product on ADDs
• Combines RUC model data with surface observations, satellite data, radar data, and PIREPS to
determine icing potential
• Provides severity and probability
Describe the safest courses of action for avoiding icing in stratiform vs. cumuliform cloud
environments correct answers • Stratiform: climb or descend
• Cumuliform: go around it
Identify the favored regions around a winter mid-latitude cyclone for the formation of snow and
other types of frozen precipitation correct answers North west of the low/ ahead of the warm
front
Describe how the temperature must change with height to produce rain, snow, sleet, or freezing.
correct answers Depends on the thickness of the layer near the surface.
Define critical thickness correct answers Thickness you need for snow/540 decameters/5,400
meters
Analyze a 1000-500mb thickness chart to determine the likelihood of rain versus snow. correct
answers The lower the thickness, the colder the better the chances of having snow Think 540 as
32 degrees mark bare minimum.
Define what is meant by ground icing "hold-over" times. correct answers • Hold-over time:
length of time deicing fluid will prevent ice build-up on an aircraft
• Time ranges from 45 minutes for frost to less than a couple minutes for freezing rain
Explain why equivalent liquid water precipitation rate is important in aviation winter weather
decision-making and how it affects hold-over times. correct answers • Basing precipitation
intensity on visibility alone does not adequately measure true rate of liquid water equivalent
accumulation
• Accurate, real-time measurements of liquid-equivalent snowfall rates need to be made and
reported to pilots and ground operations personnel, not just visibility measurements.
• Accurately predicting deicing hold-over times remains a significant aviation safety factor
Identify the fundamental cause of icing correct answers • Liquid water droplets +5 to -40c
Rime ice correct answers small droplets, freeze rapidly cause trapped air, opaque appearance,
forms at temps below -15C
clear ice correct answers larger droplets with little trapped air, forms at 0 to -5 C, equivalent to
freezing rain
mixed Ice correct answers Mixed: drop size varies, forms at intermediate temps -5 to -15C
Describe the impacts of icing on aircraft performance (stall speed, fuel consumption, service
ceiling, stall angle, etc) correct answers • Stall speed increases
• Fuel rate consumption increases
• Service ceiling decreases
• Stall at lower angle of attack than normal
• Friction increases
, Describe the effects exposure time on ice buildup. correct answers • Longer exposure time =
more icing
Describe the relationship between wing size and performance degradation due to icing correct
answers Thin wings collect more ice than large wings
• A large transport aircraft will build proportionally less ice than a small aircraft going through
the same icing region
Describe super-cooled large droplets (SLDs) and runback icing as well the hazards they pose
correct answers Small ice crystals form within droplet which may cause the entire drop to freeze
Causes a large freezing cluster of ice to form on a surface
Identify the favored areas for icing near mountains correct answers • Worst icing near the peaks
and windward side
Describe the range of temperatures and relative humidities where icing is most commonly
observed. correct answers • Most common between 0C and -40C; in-cloud humidity 70-100%
• Mountains (orographic lift), cumulus clouds and thunderstroms (strong updrafts), areas of sleet
• NW of the low, ahead of the warm front, and near the cold front
Identify the icing severity/intensity level where deicing/anti-icing equipment become ineffective.
correct answers Severe: found in stratus clouds / downwind of large bodies of water, and when
the clouds are lifted by convection over water or mountains, they become stratocumulous. That
can mean thick layer of mixed, clear, and rime icing
Identify the requirements for sustaining icing in a mixed cloud environment. correct answers
Updrafts, super-cooled liquid droplets, low temperature
Describe the safest courses of action for avoiding icing in stratiform vs. cumuliform cloud
environments correct answers Highest liquid water content at cloud top
Decode basic icing symbols. correct answers Slight - 1 bar
Moderate - 2 bars
Severe - 3 bars
Describe the CIP correct answers • Current Icing Conditions, uses PIREPs, forecasts, and
observations
• Current icing potential; FAA supplementary product on ADDs
• Combines RUC model data with surface observations, satellite data, radar data, and PIREPS to
determine icing potential
• Provides severity and probability
Describe the safest courses of action for avoiding icing in stratiform vs. cumuliform cloud
environments correct answers • Stratiform: climb or descend
• Cumuliform: go around it
